华北地台南缘张士英岩体的锆石SHRIMP U-Pb测年、Hf同位素组成及其地质意义

张士英岩体位于华北地台南缘,岩石类型包括钾长花岗岩、似斑状花岗岩和石英斑岩脉,其中只在钾长花岗岩中发育有暗色岩石包体,在包体和寄主岩中发育反映岩浆混合作用的岩石结构。钾长花岗岩、似斑状花岗岩和石英斑岩脉的SHRIMP锆石U-Pb年龄分别为107.3±2.4Ma、106.7±2.5Ma和101±3Ma。锆石Hf同位素分析结果显示,钾长花岗岩的锆石εHf(t)为-15.96～-20.80,单阶段模式年龄(tDM1)为1396～1643Ma,两阶段模式年龄(tDM2)为1880～2018Ma;似斑状花岗岩的锆石εHf(t)为-18.97～-22.18,tDM1为1512～1640Ma,tDM2为1925～2080Ma;除了一粒年龄为2.6Ga的锆石具有εHf(t)为-0.71、tDM1为2943Ma和tDM2为3036Ma的组成,石英斑岩的锆石εHf(t)为-23.41～-27.95,tDM1为1678～1896Ma,tDM2为2144～2330Ma。这些数据暗示,除了存在少量太古宙地壳物质的贡献外,张士英岩体的物质来源可能主要为1.9～2.3Ga期间形成的新生地壳,但也不排除古老地壳与富集地幔源混合的可能。综合分析前人研究成果表明,在太平洋板块俯冲方向发生转变的过程中,先存断裂带发生拉张。张士英岩体与中国东部同期岩浆活动一起可能形成于这种受断裂带控制的伸展环境。     

阿尔泰南缘早泥盆世康布铁堡组的SIMS锆石U-Pb年龄及其向东向北延伸的范围

麦兹火山-沉积盆地康布铁堡组的年龄及其东界,以及阿尔泰南缘早泥盆世火山活动往东往北延伸的范围仍然没有确定;康布铁堡组火山岩的源岩及其形成的构造环境还有待阐明。近年来在麦兹盆地东侧发现了萨吾斯铅锌矿床,矿床赋存于康布铁堡组火山岩,与别斯萨拉玢岩体密切有关。本研究对萨吾斯铅锌矿床的康布铁堡组流纹岩和别斯萨拉玢岩进行了SIMS锆石U-Pb定年以及主微量元素组成测定,以期回答上述问题。流纹岩锆石的18个靶点给出了一致的谐和年龄和加权平均年龄(401Ma);花岗闪长玢岩锆石的15个靶点给出了一致的谐和年龄和加权平均年龄(401Ma)。因此,萨吾斯铅锌矿床康布铁堡组流纹岩和别斯萨拉玢岩是同期喷发/侵入的;康布铁堡组火山活动的时代在早泥盆世;麦兹火山-沉积盆地的东界应抵达卡拉先格尔断裂西侧。在～400Ma时期,阿尔泰地区不仅存在着广泛的花岗岩类深成岩浆活动,也发生了强烈的酸性火山喷发,两者共同构成了阿尔泰南缘的大陆边缘岩浆弧。但是,火山喷发主要集中于阿尔泰南缘,受断裂控制。花岗闪长玢岩的一些锆石给出513.8Ma和3134Ma的U-Pb年龄,反映区内陆壳由寒武纪—奥陶纪岩石组成,并且还有前寒武纪微陆块。硅-碱、SiO_2-K_2O、logτ-logσ、SiO_2-FeO/(FeO+MgO)图以及构造环境判别图表明,萨吾斯铅锌矿床的流纹岩、凝灰岩、石英闪长玢岩-花岗闪长玢岩以及阿尔泰南缘早泥盆世康布铁堡组火山岩形成于活动大陆边缘或岛弧环境。康布铁堡组中下段细碧角斑岩在岛弧海底环境喷发,上段流纹岩喷发于大陆边缘环境。原始地幔标准化的多元素蛛网图表明,萨吾斯矿床的三类岩石具有明显的Nb、Ta、Ti和Sr、P、Ba负异常,显著富集Th、U、K、La、Ce、Pr、Zr、Hf。结合锆石U-Pb年龄,作者认为它们的源岩应以寒武纪-奥陶纪的岛弧岩石为主;同时,可能还含有一定比例的前寒武纪古老陆壳岩石。冲乎尔、克兰、麦兹三个火山-沉积盆地在所属构造单元、陆壳基底、火山岩岩石地球化学以及沉积岩的比例上都表现出系统变化,这些变异控制了阿尔泰南缘块状硫化物矿床从西部到中部到东部的成矿元素组合上的变化。     

Towards a Better Understanding of a Hydrodynamic Plasma-Gas Coupling by Charge Exchange Processes

Previous models of the interaction of the solar and interstellar hydrodynamic flows have clearly recognized the need to correctly describe the charge-exchange induced coupling of these flows. Neutral atoms and protons are coupled by mass-, momentum-, and energy- exchange terms due to charge exchange collisions between ionized and neutral particle species. However, treating as implified case of this problem, namely the penetration of an H-atom flow through the plasma wall ahead of the heliopause, we demonstrate that the exchange terms previously used in hydrodynamic treatments lead to a singularity with an O-type critical point at the sonic point of the H-atom flow. At this point a continuous integration of the hydrodynamic set of differential equations is impeded. We show that the remedy of this problem is given by a more accurate formulation of the momentum exchange term for the regime of quasi- and sub-sonic H-atom flows. Using a momentum exchange term derived from basic kinetic Boltzmann principles we now obtain a characteristic equation with an X-type critical point which allows to present a continuous solution from supersonic to subsonic flow conditions. Under these new auspices the already often treated problem of the penetration of interstellar H-atoms into the inner heliosphere has urgently to be revisited, since H-atoms are more effectively decelerated at their penetration into the inner heliosphere and are more strongly deflected to the flanks of the heliopause. This revised version was published online in July 2006 with corrections to the Cover Date.     

Propagation of the geomagnetic density and temperature effect into the exosphere

The propagation of the geomagnetic effect into the exosphere is investigated based on a free-flight particle kinetic model of exospheric densities and temperatures. Exobasic neutral gas conditions and their variations during a geomagnetic storm occurrence are adopted as given by the OGO-6 model. The contributions of particles originating at different exobasic locations to the density and temperature at exospheric regions are taken into account according to the time needed to reach these regions. A short-time geomagnetic variation of exobasic conditions is simulated by a Gaussianshaped A_p -index variation with an FWHM of 20 min. It is then shown that the relative amplitude and the half width of the geomagnetic density variation increase strongly with exospheric heights. The density peak and the main temperature peak are shown to be delayed by more than one and two hours, respectively, at heights above 10,000 km. The temperature variation changes from a singlepeaked to a double-peaked structure at greater exospheric heights. It is shown that the exospheric density response to geomagnetic disturbances is detectable in observations of the geocoronal He-1-584 Å resonance radiation.     

Pickup interstellar helium ions in the region of the solar gravitational cone

Our numerical analyses of the velocity and spatial distributions of pickup interstellar helium ions in the region of the solar gravitational cone in the ecliptic plane at a distance of 1 AU show that the ion density maximum must be displaced relative to the neutral helium cone axis in the direction of the Earth’s revolution around the Sun. The solar wind parameters in the numerical model correspond to their observed values during the crossing of the helium cone by the ACE spacecraft in 1998. At these parameters, the calculated angular displacement is 5°. The absence of a similar displacement in the ACE measurements is shown to stem from the fact that the spectrometer onboard ACE records and identifies only a fraction of the pickup helium ions with fairly high magnitudes and certain directions of the velocities.     

Revised interstellar neutral helium/hydrogen density ratios and the interstellar UV-radiation field

The data deduced from the UV-spectroscope on theCopernicus satellite strongly suggest that the most important ionization source in interstellar space near the solar system is a UV radiation field originating from B-stars. Adopting this hypothesis, we have used the ionization state of several elements in the interstellar medium observed byCopernicus to determine the required radiation field. From this, the degree of ionization of elements that could not be observed byCopernicus is estimated.It is shown that this interpretation of thecopernicus data can be made consistent with neutral interstellar hydrogen densities inferred from extraterrestrial L observations and with electron densities deduced from pulsar dispersion measures. Furthermore, it is shown that the ratio of neutral interstellar helium to neutral interstellar hydrogen is likely to be 2 to 3 times as large as the cosmic abundance ratio of these elements. The possibility that this ratio is about 10 times as large, meaning equal interstellar neutral hydrogen and helium densities near the solar system, cannot be ruled out. It would, however, require an interstellar radiation temperature near 9000 K. A comparison of the intensity of the interplanetary back scattered He 584 Å and the H 1216 Å radiation would lead to a direct determination of this ratio provided the solar radiation at these lines is known.     

About universes with scale‐related total masses and their abolition of presently outstanding cosmological problems

The most recently celebrated cosmological implications of the cosmic microwave background studies with WMAP (2006), though fascinating by themselves, do, however, create some extremely hard conceptual challenges for the present‐day cosmology. These recent extremely refined WMAP observations seem to reflect a universe which was extremely homogeneous at the recombination age and thus is obviously causally closed at the time of the cosmic recombination era. From the very tiny fluctuations apparent at this early epoch the presently observable nonlinear cosmic density structures can, however, only have grown up, if in addition to a mysteriously high percentage of dark matter an even higher percentage of dark energy is admitted as drivers of the cosmic evolution. The required dark energy density, on the other hand, is nevertheless 120 orders of magnitude smaller then the theoretically calculated value. These are outstanding problems of present day cosmology onto which we are looking here under new auspices. We shall investigate in the following, up to what degree a universe simply abolishes all these outstanding problems in case it reveals itself as an universe of constant total energy. As we shall show basic questions like: How could the gigantic mass of the universe of about 10⁸⁰ proton masses at all become created? – Why is the presently recognized and obviously indispensable cosmic vacuum energy density so terribly much smaller than is expected from quantum theoretical considerations, but nevertheless terribly important for the cosmic evolution? – Why is the universe within its world horizon a causally closed system? –, can perhaps simply be answered, when the assumption is made that the universe has a constant total energy with the consequence that the total mass density of the universe (matter and vacuum) scales with . Such a scaling of matter and vacuum energy abolishes the horizon problem, and the cosmic vacuum energy density can easily be reconciled with its theoretical expectation values. In this model the mass of the universe increases linearly with the world extension R_u and can grow up from a Planck mass as a vacuum fluctuation. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Interstellar pickup protons and solar wind heating in the outer heliosphere

The ionization of hydrogen atoms that penetrate into the heliosphere from the interstellar medium gives rise to a peculiar population of energetic protons (interstellar pickup protons) in the solar wind. The short-wavelength Alfvènic turbulence in the outer heliosphere is entirely attributable to the source associated with the instability of the initial anisotropic pickup proton velocity distribution. The bulk of the generated turbulent energy is subsequently absorbed by the pickup protons themselves through the cyclotron-resonance particle-wave interaction, and only an insignificant fraction of this energy can be transferred to the solar wind protons and heat them up.